New in Symfony 4.3: Default and Trim Env Var Processors

Env Var processors allow to transform the value of environment variables
before using them in the Symfony app configuration. They are useful for example
to transform the type of the env var (which, by definition is always a string)
into a more suitable type, such as an integer or a boolean. In Symfony 4.3 we
added new processors to provide new transformations.

It returns a default value when the given env var is not defined. It uses this
syntax: env(default:DEFAULT_VALUE:ENV_VAR_NAME). You can combine it with any
of the other env vars to do advanced things like the following: